Human eyesight is a product of two separate processes that work together to form images for a person to “see”. One of these processes, herein referred to as the physical component, concerns the physical structure of the various elements of the eye and how incoming light is manipulated and processed by the eye. Defects in the shape of the cornea, the retinal wall, or the optic nerve can impair or destroy the functionality of a person's eye and thus impair or eliminate the ability to perceive images. Fortunately, defects in the cornea of a person can be corrected through the use of glasses, contacts, or surgery such as laser keratotomy. Likewise, defects in the retina of a person might be often repairable by surgery.
The second process involved in allowing humans to see images is herein referred to as the neurological component. This component concerns neural processing in the brain and how the brain analyzes information sent from the eyes to produce an image. A person can likewise have a number of defects in this component of the visual process, such as reduced visual acuity, reduced sensitivity for spatial contrast, reduced vernier acuity, spatial distortion, abnormal spatial interactions and impaired contour detection.
The physical component and the neurological component work together to form images that a person sees, or more precisely, that a person perceives.
A visual system is classically described as a hierarchy of visual processing stages (though recent views emphasize backward projections), starting from light detection and transduction in the eye (i.e. photoreceptors) through several stages of spatial integration, each stage forming receptive fields of increasing complexity. An important stage in image analysis, in the primary visual cortex, includes receptive fields (units) that are sensitive to image contrast that varies in a specific direction (orientation selectivity) on a specific scale (size selectivity). Human contrast sensitivity is best described by the aggregate response of these units (filters).
Recent research (psychophysics, physiology) points to spatial interactions between oriented receptive fields as an important factor in modulating activity of the corresponding neuronal units. Local contrast sensitivity can be increased or decreased depending on the light distribution within neighboring locations. More specifically, facilitation of oriented contrast detection is obtained by presenting for example a target flanked by collinear, high contrast stimuli at an optimal distance. Levels of neuronal suppression can be obtained by presenting the target with more proximal co-oriented flankers.
Responses of individual neurons to repeated presentations of the same stimulus are highly variable (noisy). Noise may impose a fundamental limit on the reliable detection and discrimination of visual signals by individual cortical neurons. Neural interactions determine the sensitivity for contrast at each spatial frequency, and the combinations of neural activities derive an individual's contrast sensitivity function (CSF). The brain pools responses across many neurons to average out noisy activity of single cells, thus improving signal-to-noise ratio, leading to substantially improved visual performance.
As for an example, the studies of Uri Polat et al. have shown that the noise of individual cortical neurons can be brought under experimental control by appropriate choice of visual stimulus conditions.
A method for identifying deficiencies and/or inefficiencies in neuronal interaction of a person's visual cortex and possibly train this person, has been disclosed in U.S. Pat. No. 6,876,758 and U.S. Pat. No. 7,007,912 in the name of U. Polat. Studies of U. Polat et al. enclose following references:    Polat, Uri and Sagi, Dov, “Plasticity of Spatial Interactions in Early Vision” Department of Neurobiology, Brain Research, the Weizmann Institute of Science, Rehovot 76100 Israel,    Levi, Dennis and Polat, Uri “Neural Plasticity in Adults with Amblyopia”, Proc. Natl. Acad. Sci. USA, Neurobiology, vol. 93, pp 6830-6834, February 1996,    Polat, Uri, “Functional Architecture of Long-range Perceptual Interactions” Spatial Vision, vol. 12, no 2, pp 143-162, 1999.
As for an example, a method called NeuroVision has been developed, based on these principles and commercialized by the Company Neurovision Inc. (Singapore) to offer eye correction training session.
A typical building block of the suggested visual stimulations is the Gabor patch, which efficiently activates and matches the shape of receptive field in the visual cortex.
Polat and colleagues have demonstrated that contrast sensitivity of adult human subjects at low levels can be increased by a factor of 2 through specific control of the Gabor patches parameters. This stimulation-control technique is called “Lateral Masking”, where collinearly-oriented flanking Gabors are displayed in addition to the target Gabor image.
In the first stage of a training session overview, the subject is exposed to a set of visual perception tasks, aimed to analyze and identify each subject's neural inefficiencies. The images are for example images presented to the patient on a monitor screen. The patient has to perform visual tasks indicating whether he/she sees a target arrangement. The indications may be made by means of a computer mouse.
A training system may analyze subject's performance. Based on said analysis, training plan can be initialized, and subject specificity can be achieved by administering patient-specific stimuli in a controlled environment. The stimuli parameters can be automatically tailored to each subject's needs; among these parameters are spatial frequencies, spatial arrangement of the Gabor patches, contrast level, orientation (local and global), tasks order, context, timing.
Each session may be designed to train, directly and selectively, those functions in the visual cortex that were diagnosed to be ineffective. At each session an algorithm may analyze the patient's responses and accordingly adjusts the level of visual difficulty to the range most effective for further improvement. Between sessions, the progress of the patient may be measured and taken into account by the algorithm for the next therapeutic session. Thus, for each subject an individual training schedule may be designed, and adapted during the training session, based on the initial state of visual performance, severity of dysfunction and progress in training.
As for an example, the training session is applied in successive 30-minute sessions, administered 2-3 times a week, a total of approximately 20-30 sessions. Every 5 sessions, subject's visual acuity may be tested in order to continuously monitor subject's progress.
A training system is usually a software-based, interactive system tailored and continuously adaptive to the individual patient's learning and improvement. The Internet can be used as a distribution media, which allows providing this personalized interactive service to a practically unlimited number of training locations.
During each training session, the patient at the clinic/investigative site can be exposed to visual images displayed on a computer monitor. The patient can interactively communicate with the computer using for example a mouse. During the session, some data that reflects patient's performance can be recorded. At the end of the session, this data can be sent to a central server. Algorithmic software, running on the server, can analyze the patient's performance and progress and can generate the parameters for the next training session.
Although clinical tests have shown that about 70 percent of the users of training such as a Neurovision training system and method have improved their eye conditions, the inventors have noticed that the efficiency of said method is not always optimal.
Accordingly there remains a need for improving the receptiveness of a person to a training session of the human visual system where visual stimuli arrangements are provided to the person.
A non-limiting example of such training session is a NeuroVision training session where arrangements are designed to modify levels of neuronal facilitation and/or levels of neuronal suppression in the person's visual cortex.